Assessment of macular function by focal electroretinogram and pattern electroretinogram before and after epimacular membrane surgery

PURPOSE: To evaluate macular function before and after surgical peeling of idiopathic epimacular membrane (EMM). METHODS: Logarithm of the minimal angle of resolution visual acuity and results of focal (central 9 x 9 degrees) electroretinogram (fERG), pattern electroretinogram (pERG), and optical coherence tomography (OCT) assessment of macular volume were evaluated for 22 eyes of 22 patients (mean age +/- SD, 63.20 +/- 10.0 years) with EMM preoperatively (baseline) and 6 months after surgical peeling. Preoperative visual acuity and fERG and pERG amplitudes observed in EMM eyes were compared with those in 15 age-matched control eyes. RESULTS: In the preoperative evaluation, EMM eyes had a significant (P < 0.01; one-way analysis of variance) reduction in visual acuity and fERG and pERG amplitudes and an increase in OCT macular volume when compared with controls. In EMM eyes, the decrease in visual acuity was significantly correlated (P < 0.01, Pearson test) to the reduction in fERG and pERG amplitudes. At the postoperative evaluation, EMM eyes had a correlated significant (P < 0.01) increase in visual acuity, fERG amplitude, and pERG amplitude with respect to the preoperative values. All EMM eyes had a significant (P <0.01) reduction in macular volume, and retinal microanatomy was restored to normal conditions. CONCLUSION: In EMM eyes, the decrease in visual acuity is related to dysfunction of both preganglionic (abnormal fERG) and ganglionic (abnormal pERG) macular elements. Surgical removal of EMM may induce improvement of the function of both outer and innermost macular retinal layers, leading to a related increase in visual acuity.